Plastic scraps, like other refuse, have come to occur in huge volumes with the growth of industry and the economy. Their volumes are steadily increasing year after year.
These plastic scraps have been so far disposed of mostly by being dumped at land reclamation sites, processed for the production of flower boxes and piles, and sorted out and reclaimed as raw material. Since they occur everyday in such huge volumes, such measures of disposal are hardly sufficient for their complete disposal. The open areas and the methods adopted for their disposal are rapidly reaching their limits.
If such methods as combustion and gasification become capable of being properly carried out, they will obviously make complete disposal of plastic scraps possible.
Unfortunately, the combustion of plastic scraps entails partial generation of heat and temperatures so high as to defy control by existing techniques of combustion and, moreover, evolves noxious gas and soot in amounts so large as to cause a public nuisance by air pollution.
There may be conceived an idea of partially oxidizing plastic scraps or thermally decomposing them at temperatures exceeding 700.degree. C. and utilizing the product of the partial oxidization or thermal decomposition as gaseous fuel. Since this operation involves pretreatments such as collection, washing, pulverization, and conveyance and necessitates installation of a reactor and a gas tank and consumption of combination air, it requires a huge cost investment in equipment and involves high operating costs. Thus, this idea is hardly practicable economically.
Plastic scraps are a poor conductor of heat. When a reaction vessel filled with plastic scraps for thermal decomposition is operated, any attempt to keep the internal temperature of the reaction vessel uniform brings about a wide difference of temperature between the internal wall and the external wall of the reaction vessel and entails deposition of carbon on the internal wall of the reaction vessel during its operation. The deposited carbon can be removed by the force exerted thereon as with a stirring rod, for example. When the amount of the deposited carbon is large, however, there is a possibility that the use of the stirring rod will generate torque even to the extent of breaking the reactor.